Use of clinker kiln dust for gas scrubbing

ABSTRACT

Methods and apparatus for reducing the content of controlled acidic pollutants in clinker kiln emissions are disclosed. The methods and apparatus include introducing bypass dust produced during production of clinker into one or more locations between the preheater exhaust and the inlet to a dust filter including into a gas conditioning tower. Total bypass dust separated from the kiln exhaust gas may be used. The bypass dust can be separated into a fine and coarse portions. Fine or total bypass dust can be mixed with water to form a bypass dust slurry that can be introduced into the gas conditioning tower. Bypass dust can be used to reduce the content of acidic pollutants such as hydrogen chloride HCl and sulfur oxides SO x  from clinker kiln emissions.

This application is a continuation of U.S. application Ser. No.15/410,007, filed on Jan. 19, 2017, now allowed, which is a Divisionalof U.S. application Ser. No. 15/229,990, filed on Aug. 5, 2016, now U.S.Pat. No. 9,597,625, which claims the benefit under 35 U.S.C. §119(e) ofU.S. Provisional Application No. 62/201,971, filed on Aug. 6, 2015, eachof which is incorporated by reference in its entirety.

FIELD

Methods and apparatus for reducing the content of controlled acidicpollutants in clinker kiln emissions are disclosed. The methods andapparatus include introducing bypass dust generated during production ofclinker into one or more locations between the preheater exhaust and theinlet to a dust filter including into a gas conditioning tower. Thetotal bypass dust can be used or the bypass dust can be separated intofine and coarse portions. Fine or total bypass dust can be mixed withwater to form a bypass dust slurry that can be introduced into the gasconditioning tower. Bypass dust can be used to reduce the content ofacidic pollutants such as hydrogen chloride HCl and sulfur oxides SO_(x)in clinker kiln emissions.

BACKGROUND

Reducing the atmospheric emission of controlled pollutants is acontinuing societal concern. In the United States primary regulatoryauthority over industrial source air emissions resides with the U.S.Environmental Protection Agency (EPA). Over the years, the EPA hasincreased the stringency of air pollution control programs, both bydecreasing the limits on acceptable emissions and by continuallyincreasing the number and types of regulated pollutants.

As a source of controlled pollutant emissions, clinker kilns are subjectto EPA emission regulations. Gaseous exhaust from a clinker kilncontains particulates and various gases. The particulates can be removedfrom the exhaust stream using a particle or dust separator such as anelectrostatic precipitator (ESP) and/or a fabric filter baghouse (FFB)collector. The filtered exhaust gases can contain acidic controlledpollutants such as hydrogen chloride HCl and sulfur oxides SO_(x) thatmust be reduced to meet regulatory requirements. In general, it isdesirable that the concentration of hydrogen chloride HCl in clinkerkiln emissions be less than 3 ppm (dry basis with 7% O₂) and thepermitted concentration of sulfur oxides SO_(x) is set for each plant.

A wet chemical scrubber can be included after a dust filter; however,conventional methods to scrub acid forming gases such as hydrogenchloride HCl and sulfur oxides SO_(x) can be expensive and inconsistentwith the economic operation of an energy-efficient clinker kiln. Forexample, conventional wet scrubbers, which commonly use spray dropletsizes greater than 1000 microns, typically use 10 gal/min to 100 gal/minof liquid to scrub 1000 standard cubic feet per minute of effluent gases(1-10 kilograms of liquid per kilogram of gas). As a result, theconsumption of water, scrubbing chemicals, and energy using conventionalwet scrubbers is high.

Hot clinker kiln exhaust gases must be cooled to approximately 150° C.to have acceptable particulate emissions from an ESP or cooled toapproximately 180° C. to protect a FFB from overheating. To cool andcondition hot kiln exhaust gases, before entering an ESP or FFB a sprayof water can be used to cool and condition the exhaust gases in a gasconditioning tower (GCT). Further cooling and conditioning may then beperformed by passing the conditioned exhaust gases through cool wetlimestone of a raw mill used to grind the raw materials into a kilnfeed, which can then be transported to a pyroprocessing kiln. A GCT canalso be used in parallel with the raw grinding transport if the moisturecontent of the raw material is high; however, a GCT is generally used inan upstream process when the moisture content of the raw material islow.

An approach to reduce hydrogen chloride HCl and sulfur oxide SO_(x)emissions from a clinker kiln is to inject a high-pH lime slurry intothe spray used in a gas conditioning tower (GCT). To prepare the limeslurry, lime can be reacted with water to form calcium hydrate Ca(OH)₂(hydrated lime). Hydrated lime Ca(OH)₂ can be introduced into a GCT indry form containing, for example, up to about 2 wt % water, or can be inthe form of a wet slurry having a hydrated lime solids content, forexample, up to about 50 wt % and introduced into the GCT as a spray ofdroplets. The lime CaO used to form the slurry is typically purchasedfrom a supplier and transported to the clinker kiln, which increases thecost of reducing emission of controlled pollutants. The lime istypically produced to be highly reactive with acid gases, which can bedetermined by a number of factors such as the pore volume, the specificsurface area, low water content, and low agglomeration. Alternatively,hydrated lime, which is stable and easier to handle, can be preparedremotely and transported to the clinker kiln. Ca(OH)₂ in the lime slurryadsorbs and reacts with sulfur oxides SO_(x) and other acid forminggases such as hydrogen chloride HCl to produce thermally stable salts,which can be filtered from the effluent gases and thereby reduceemissions of the acid forming species in the exhaust gases.

It is desirable to find alternative ways to reduce controlled acidicpollutants in clinker kiln emissions to meet the continuously evolvingenvironmental standards.

SUMMARY

Methods for reducing the concentration of controlled acidic pollutantsin clinker kiln emissions are disclosed, comprising providing a clinkerkiln, wherein the clinker kiln comprises a gas conditioning systemconfigured to process exhaust gases from the clinker kiln; andintroducing bypass dust generated during operation of the clinker kilnat one or more locations in the gas conditioning system, to reduce theconcentration of controlled pollutants in the clinker kiln emissions.

According to the present invention, methods for reducing theconcentration of controlled pollutants in clinker kiln emissionsprovided by the present disclosure comprise providing a clinker kiln,wherein the clinker kiln comprises a gas conditioning system configuredto process exhaust gases from the clinker kiln; and introducing bypassdust generated during operation of the clinker kiln at one or morelocations in the gas conditioning system, to reduce the concentration ofcontrolled pollutants in the clinker kiln emissions.

According to the present invention, a clinker plant provided by thepresent disclosure comprises a gas conditioning system comprising apreheater exit, a gas conditioning tower, and a main baghouse; one ormore separators for separating dust generated during the production ofclinker into one or more fractions; and introducing at least one of theone or more dust fractions into the gas conditioning system at one ormore locations between the preheater exit and the main baghouse.

According to the present invention, methods for reducing theconcentration of controlled pollutants in clinker kiln emissions,comprise providing a clinker kiln, wherein the clinker kiln comprises agas conditioning system configured to process exhaust gases from theclinker kiln; and introducing dust generated during operation of theclinker kiln at one or more locations in the gas conditioning system, toreduce the concentration of controlled pollutants in the clinker kilnemissions.

According to the present invention, a clinker plant comprises a gasconditioning system comprising a preheater exit, a gas conditioningtower, and a main baghouse; a separator for separating dust from exhaustgases; and a nozzle for introducing the separated dust in proximity tothe preheater exhaust exit, into the gas conditioning tower, inproximity to the inlet to the dust collector, or a combination of any ofthe foregoing.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only. Thedrawings are not intended to limit the scope of the present disclosure.

FIG. 1 is a schematic diagram showing certain components of a prior artclinker kiln.

FIG. 2 is a graph showing the moles of Ca in the form of free lime CaOor hydrated lime Ca(OH)₂ needed to reduce the HCl content in emissionsto the indicated ratio.

FIG. 3 is a graph showing the moles of Ca in the form of free lime CaOor hydrated lime Ca(OH)₂ needed to reduce the SO_(x) content inemissions to the indicated ratio.

FIG. 4 is a graph showing the particle size distribution forcompositions used to scrub controlled acidic pollutants from clinkerkiln emissions.

FIG. 5 is a schematic diagram showing certain components of a clinkerkiln including a system for removing bypass dust from the clinker kilnriser and for introducing the bypass dust into the gas conditioningsystem for scrubbing acidic pollutants from the clinker kiln exhaust asprovided by certain embodiments of the present disclosure.

FIG. 6 shows a flow diagram of a controlled pollutant scrubbing systemusing bypass dust as provided by certain embodiments of the presentdisclosure.

FIG. 7 shows a flow diagram of an alternative controlled pollutantscrubbing system using bypass dust as provided by certain embodiments ofthe present disclosure.

FIG. 8 shows the molar ratio of HCl emissions to potential Ca(OH)₂ withpotential Ca(OH)₂ input using lime or bypass dust injection to removecontrolled pollutants from clinker kiln exhaust.

FIG. 9 shows the molar ratio of hydrogen chloride HCl emission topotential Ca(OH)₂ with potential Ca(OH)₂ input using lime or bypass dustinjection to remove controlled pollutants from clinker kiln exhaust.

FIG. 10 shows the molar ratio of sulfur oxides SO_(x) emission topotential Ca(OH)₂ with potential Ca(OH)₂ input using lime or bypass dustinjection to remove controlled pollutants from clinker kiln exhaust.

FIG. 11 shows the molar ratio of sulfur oxides SO_(x) emission topotential Ca(OH)₂ with potential Ca(OH)₂ input using lime or bypass dustinjection to remove controlled pollutants from clinker kiln exhaust.

Reference is now made in detail to embodiments of the presentdisclosure. While certain embodiments of the present disclosure aredescribed, it will be understood that it is not intended to limit theembodiments of the present disclosure to the disclosed embodiments. Tothe contrary, reference to embodiments of the present disclosure isintended to cover alternatives, modifications, and equivalents as may beincluded within the spirit and scope of the embodiments of the presentdisclosure as defined by the appended claims.

DETAILED DESCRIPTION

Methods and apparatus for reducing emissions of controlled pollutantsfrom clinker kilns are disclosed. Dust having a high free lime CaOcontent generated during clinker production is fed into the kiln exhaustbetween the preheater exit and the main vent baghouse inlet to reducethe concentration of controlled acidic pollutants such as hydrogenchloride HCl and sulfur oxides SO_(x) in the kiln emissions.

Certain aspects of a clinker kiln are shown in FIG. 1. A primary kilnfeed material comprising a calcium-containing mineral used inmanufacturing clinker is obtained from a quarry. The primary feedmaterial is limestone, to which smaller quantities of sand, clay, shale,iron ore, bauxite and/or other materials which provide the calcium,silica, aluminum and iron necessary to produce clinker can be added. Thequarried material is reduced in size by a crusher (not shown), and thecrushed raw material is then transported to the raw grinding area of theclinker kiln system. Suitable proportions of the raw materials are thenmixed and further reduced in size in a raw mill to form a kiln feed.

In operation, a raw mill continuously classifies the kiln feed beingprocessed using separation techniques such as cyclones, swirl cageclassifiers, or other third and fourth generation classifiers. Largediameter particles can be retained for further grinding and smaller,properly sized particles can be sent on for further processing. Veryfine dust particles become entrained in the gas flow and can be removedby a dust filter such as an ESP or FFB.

The kiln feed from the raw mill is transported to and preheated usingexhaust gas from the kiln in a preheating tower 1, comprising a seriesof vertically stacked cyclone chambers 2 and a precalciner 3. As shownin FIG. 1, kiln feed enters at the top of the preheating tower 1 and ispreheated as it descends through the preheating tower 1 under the forceof gravity. The heated kiln feed is then introduced into a precalciner3, which converts the calcium carbonate (CaCO₃) in the limestone (orother feed material) into calcium oxide (CaO, also referred to as freelime), releasing a large amount of carbon dioxide (CO₂) in the process.During precalcination the kiln feed is heated to a high temperaturebetween about 800° C. and 900° C. and the gas temperature can be fromabout 900° C. to about 1,000° C. The energy required for precalcinationis higher than the energy content of the kiln exhaust gases, andtherefore additional heat is generated in the precalciner.

After precalcination, the precalcined kiln feed is introduced into arotary pyroprocessing kiln, such as rotary kiln 5 where the kiln feed isheated to a temperature of about 1,500° C. to form clinker, consistingprimarily of calcium silicates. The kiln feed is introduced through aseparate line and gases carrying dust leave the kiln through kiln exitriser duct 4. Rotary kiln 5 is substantially horizontal, with a slighttilt sufficient for gravity-assisted transport of the materialsundergoing pyroprocessing along its length. The hot clinker is thendischarged from the rotary kiln into a cooling chamber (not shown).After being cooled, the clinker is discharged from the cooling chamberand interground with gypsum and other mineral additives to producecement.

Clinker kilns are designed for maximum efficiency to make optimal use ofthermal energy. Gases are routed through the plant so as to use andrecapture as much of the heat as possible. Accordingly, the physicallayout of a clinker kiln is optimized to minimize heat losses as thematerials travel between the various processing stations in the system.For example, exhaust gases from rotary kiln 5 are used to preheat anddry the kiln feed before pyroprocessing in preheating tower 1. Asevident in FIG. 1, the gas flow through the plant is generally counterto the flow of the solids and, from the time the gases leave the kiln tothe time they are exhausted into the atmosphere, the gases exchange heatwith the kiln feed, i.e., the gases are cooled as the kiln feed is driedand heated. Thus, for example, the kiln feed is progressively heated asit travels down the preheating tower 1 from one preheating cyclone 2 tothe next, while the flue gases become successively cooler as they travelup the preheating tower.

The air used for combustion in rotary kiln 5 first flows through acooling chamber (not shown), where the air heats as it cools theclinker. The hot exhaust gases from kiln 5 flow through the precalciner3 and through the preheating tower 1. After combustion in the kiln verylittle oxygen remains in the exhaust gas flow, and so additional air isintroduced into precalciner 3 to support combustion. After passingthrough preheating tower 1, the temperature of the exhaust gases A isreduced by routing through GCT 15 that can include water 19 sprayed fromnozzles 18. The exhaust gases containing entrained dust and volatilegases B are then filtered using a baghouse 17 or an electrostaticprecipitator. The filtered dust is typically recycled back into andblended with the kiln feed.

FIG. 1 also shows a pollution control system comprising, for example, ahydrated lime Ca(OH)₂ slurry source 21 and a controllable slurryinjector 20 to add a controlled quantity of the hydrated lime slurry tothe liquid sprayed from nozzles 18. The slurry source 21 can comprisealkaline earth materials, such as hydrated lime, having a small particlesize. Commercially available sources of fine, dry hydrated lime may beproduced by a variety of methods. Fine, dry particles of hydrated limecan have particle sizes on the order of 10 microns and, therefore canhave a relatively large surface area to facilitate surface chemicalreactions. However, commercially available sources of dry particles ofchemically active hydrated lime can be comparatively expensive. Use offine, dry hydrated lime particles also presents an added difficultybecause dry hydrated lime must be stored in an inert environment untiluse because of its high chemical reactivity. Specifically, atmosphericcarbon dioxide readily reacts with hydrated lime to form calciumcarbonate, according to the expression: Ca(OH)₂+CO₂→CaCO₃ (s)+H₂O (l).Compared to hydrated lime, calcium carbonate is comparatively unreactivewith pollutants such as acid-forming gases.

The hydrated lime slurry can be prepared on-site substantially as neededusing an in-line grinder to ensure the highest chemical reactivity ofthe ground hydrated lime particles in the slurry. If the slurry is notimmediately used, it may be maintained in an inert ambient environment,such as a sealed or nitrogen purged storage tank. If the slurry isstored in an inert ambient environment, it may be stored for relativelyshort periods (e.g., less than 24 hours) without substantiallydecreasing its chemical reactivity. Alternatively, the hydrated limeslurry may be transported to the site and mixed with water prior to use.

The spray from the nozzles 18 may be adjusted to achieve a desiredcooling, for example, reducing the gas temperature from about 400° C. to150° C. for ESP scrubbing or to about 180° C. for FFB scrubbing. Thetotal quantity of spray can be as low as possible and the evaporativelifetime of the spray droplets can be short. The droplet size can beadjusted such that the droplets completely evaporate just before exitingthe GCT. The mean lifetime of the spray droplets can be, for example,slightly less than the transit time of gases through the GCT. Forexample, the spray can be adjusted such that the largest spray dropletshave a diameter from about 120 microns to about 150 microns. Theevaporative lifetime of a spray droplet can be within a range from about2 seconds to about 5 seconds. This is a relatively short time period foracidic gases to adsorb on to the surface of a droplet, be absorbed intothe droplet, and react with calcium hydroxide released from the slurryparticles in the droplet. For the reaction to be rapid and efficient, itcan be desirable that the hydrated lime particles suspended in the spraydroplets substantially dissolve during the transit time of the droplet.

For the spray to efficiently scrub the kiln exhaust the individualdroplets should rapidly absorb pollutant gases and hydrated limeparticles contained by the droplets should rapidly react with the acidicpollutant gases before the droplets evaporate within the GCT.Additionally, chemical scrubbing agents and reacted products shouldotherwise be compatible with the economic operation of the clinker kiln.It is desirable that the cost of the chemical scrubbing agent should below and the chemical scrubbing agent and reacted products not damage orclog pipes, valves, or fittings in the clinker kiln. It is alsodesirable that any scrubbing chemical used not contaminate the kiln feedor adversely alter the chemical balance of the kiln feed.

Flow of water or hydrated lime slurry to the nozzles 18 can be adjustedto provide efficient scrubbing. The nozzles facilitate efficientscrubbing by providing droplets characterized by a large initialsurface-to-volume ratio, such that the adsorption of gases is rapid;provide uniform chemical reaction dynamics by maintaining asubstantially similar initial droplet diameter among the droplets andhence substantially the same quantity of slurry particles; and, becausethe droplets initially have about the same size, will have a similarlifetime in the GCT from about 1 second to about 5 seconds, depending onthe design and throughput of a particular GCT. The median droplet sizecan be adjusted such that the droplets evaporate near the exit of theGCT. Finely ground hydrated lime particles with a particle diameter inthe range of 1 micron to 25 microns can be highly chemically reactive,in part because the particles have an extremely large surface arearelative to the volume. The large surface-to-volume ratio of thehydrated lime particles increases the rate at which calcium hydroxidedissolves in the spray droplets. Decreasing the particle diameter ofhydrated lime particles substantially below 25 microns facilitatesfaster dissolution of the hydrated lime particles. The release ofcalcium hydroxide from the dissolving hydrated lime particles can occurat a sufficiently rapid rate that the release rate does not limit thereaction that converts absorbed acidic gases into salts. For common GCTevaporative lifetimes of 1 second to 5 seconds, the hydrated limeparticles can have a diameter less than about 10 microns such that thehydrated lime particles substantially dissolve in the spray dropletswithin the GCT before evaporation.

Also, for effective scrubbing, a high pH spray is desirable because ofreduced solubility of ammonia in the high pH spray droplets. In clinkerkilns the absorption of ammonia is undesirable, because ammonium sulfatesalts are not thermally stable at typical GCT temperatures greater thanabout 235° C. Any ammonium sulfate formed in a droplet will decomposewhen the droplet evaporates, re-releasing ammonia and sulfur dioxide.This reduces the efficiency of the reactions that convert acidic gasesinto thermally stable salts. The efficiency of the scrubbing processthus increases when the quantity of hydrated lime is such that thedroplets retain a high pH during their evaporative lifetime in the GCT.

As an alternative to injecting hydrated lime either dry or in the formof a slurry obtained from commercial sources in relatively pure forminto a GCT to reduce the emissions of controlled pollutants in a clinkerkiln, dust generated during the clinker manufacturing process can beused in the same manner to efficiently and cost-effectively reduce theemissions of controlled acidic pollutants. The dust or particulates usedto reduce controlled acidic pollutants as provided by the presentdisclosure is referred to as “bypass dust.” Bypass dust refers toparticulates generated during production of clinker. Clinker kiln bypassdust contains a high content of chlorides, sulfates, and calcium oxideCaO (free lime). The calcium oxide CaO in the bypass dust can serve asan efficient absorbent of controlled acidic pollutants such as HCl,SO_(x), and H₂SO₄ contained in clinker kiln preheater exhaust gases. Thebypass dust can originate and be extracted from any suitable stage inthe clinker production process such as at the kiln riser duct betweenthe precalciner and the rotary kiln. The generation of bypass dust takesplace during the clinker production process and therefore transportationand storage costs can be reduced compared to the use of commercial limewhich must be shipped to the kiln. Bypass dust can be used to reduce theemission of controlled pollutants in a clinker kiln at least aseffectively and as efficiently as commercial hydrated lime. Bypass dustis also referred to as dust.

Controlled pollutants in kiln exhaust can adsorb onto dry lime CaOparticulates and/or onto hydrated lime Ca(OH)₂ and/or onto lime slurrydroplets containing Ca(OH)₂ in the GCT. Binding and transport to thesurfaces is expected to be more likely on humid or wet surfaces.However, adsorption of controlled acidic pollutants also occursefficiently on dry particulate surfaces. Following adsorption,pollutants such a HCl and SO_(x) can react with CaO or Ca(OH)₂ to form,for example, CaCl₂, CaSO₃, and/or CaSO₄.

Measurements using hydrated lime as a scrubbing material indicated thatat an injection rate of about 730 lb/h the SO_(x) emission was from 22.4ppm to 36.3 ppm and the HCl emission was from 4.38 ppm to 5.0 ppm. At aninjection rate of 1,670 lb/h the SO_(x) emission was from 22.4 ppm to30.8 ppm and the HCl was from 3.3 ppm to 4.3 ppm. Increasing the rate atwhich hydrated lime was injected into the GCT reduced the concentrationof SO_(x) and HCl in the emissions even further. Based on these andother measurements, it was determined that from about 230 mol to about490 mol of Ca adsorbed about 1 mol of HCl, and from about 7 mol to about108 mol of Ca adsorbed about 1 mol of SO_(x).

These measurements were made for a particular clinker kiln system andusing particular raw material. It will be appreciated that the valuesfor the various parameters can vary depending on a number of factorsthat can be established for a particular clinker kiln plant and can beadjusted during operation.

The reduction of HCl emissions with moles of Ca needed to produce a 1mol reduction in HCl is shown in FIG. 2. In FIG. 2, 0.1 indicates a 90%reduction in HCl concentration, for example, from 50 mol/h to 5 mol/h,0.2 indicates an 80% reduction in HCl concentration, and so forth. InFIGS. 2 and 3 bypass dust refers to bypass dust taken directly from theexit kiln riser that has not be separated into size fractions, limerefers to commercially obtained dry calcium hydroxide Ca(OH)₂, and theslurry refers to commercially obtained hydrated lime Ca(OH)₂ slurry.

Referring to FIG. 2, injecting a hydrated lime slurry having a solidscontent of about 45% had the best efficiency and reduction in HClconcentration. The results demonstrated that the use of bypass dustrather than dry lime when introduced into the exhaust gases at asuitable rate can reduce HCl emissions at least to the same extent ashydrated lime. It was noted that reducing HCl concentrations was moreefficient at lower temperatures; however, other factors also appeared toaffect the HCl scrubbing efficiency.

The reduction in SO_(x) emissions with moles Ca injected into the kilnexhaust gases is shown in FIG. 3. As with HCl emissions, at certain Caconcentrations, bypass dust is at least as effective in reducing SO_(x)concentration in kiln exhaust gas as is dry lime.

In summary, it was possible to produce a slurry from fine bypass dustthat exhibited an HCl and SO_(x) scrubbing efficiency on a moles Cabasis similar to that of a conventional hydrated lime slurry.

The results presented in FIGS. 8-11 demonstrate that on a CaO or Ca(OH)₂basis, bypass dust is more efficient than lime at removing hydrogenchloride HCl and sulfur oxides SO_(x) from kiln exhaust. Furthermore,the way in which bypass dust is injected into the GCT such as thelocation of injection and the manner of injection can further improvethe scrubbing efficiency of bypass dust.

The data presented in FIG. 2 and FIG. 3 demonstrate that bypass dust isan effective alternative to hydrated lime for controlling HCl and SO_(x)emissions. Bypass dust has a specific surface area that is about threetimes smaller than that of hydrated lime and has significantly lessporosity. Furthermore, only about 28% of the mass of bypass dust is freeCaO. Nevertheless, the bypass dust was demonstrated to be effective inreducing the emissions of acidic pollutants. It is possible that othercomponents of the bypass dust increase the adsorption of HCl and SO_(x),and thereby also contribute to the scrubbing efficiency.

FIG. 4 shows the particle size distribution of a dry lime composition, ahydrated lime slurry and three bypass dust compositions. FIG. 4 showsthat the size of the fine bypass dust comprises particles having aboutthe same size as the particles in typical dry and wet lime slurries ofabout 5 microns to about 10 microns. The dry lime composition wascharacterized by a specific surface area of 2.23 derived from theparticle size distribution, which was similar to that of the wet bypassdust slurry of 2.50. The specific surface area of the fine dry bypassdust used to make the dust slurry was 5.05, which is significantlygreater than that of the dry fine wet particles in the slurry,indicating that the particles forming the bypass dust swell and/oragglomerate upon exposure to water. It should be appreciated that theparticulars of the particle size distribution, specific area, and meanparticle diameter can vary depending on the source, and in the case ofbypass dust on the particular clinker kiln, source material, and otherparameters.

Hydrated lime product such as the commercial dried lime and hydratedlime are characterized by a mean particle size distribution less thanabout 10 microns, a wide range of particle diameters from about 0.05microns to about 50 microns, and a specific surface area from about 2.1to about 2.6. The fine bypass dust preparations used to obtain theresults presented in FIGS. 2 and 3, exhibited a narrower, somewhatGaussian, particle size distribution with a mean particle diameter ofabout 9 microns. When hydrated, the hydrated fine bypass dust particlesize distribution remained essentially Gaussian but the mean particlediameter increased to about 20 microns. The specific surface areadecreased from about 5.05 to about 2.23. Despite the larger meanparticle diameter, the fine bypass dust slurry is expected to be atleast as effective as commercially obtained hydrated lime in reducingHCl and SO_(x) in clinker kiln emission due to the similar chemistry andparticle size distribution. As demonstrated by the results presented inFIGS. 8-11, fine bypass dust slurry and total bypass dust slurry exhibitsimilar scrubbing efficiencies for hydrogen chloride HCl and for sulfuroxides SO_(x) as a commercial lime slurry.

Fine bypass dust can be characterized by an average mean particlediameter from about 2 microns to about 40 microns, and the total bypassdust is characterized by an average mean particle diameter from about 20microns to about 80 microns. In certain embodiments, fine bypass dust ischaracterized by an average mean particle diameter less than about 100microns, and a coarse bypass dust is characterized by an average meanparticle diameter greater than about 100 microns. Also, bypass dustwhether dry or in the form of a slurry can include any suitable particlesize distribution for efficiently scrubbing controlled acidic pollutantsfrom clinker kiln emissions. Particle size can be measured, for example,using a Beckman Coulter LS 13 320 laser diffraction particle sizeanalyzer.

It was also determined that fine bypass dust slurries are rheologicallystable up to a solids content of about 65 wt %, where wt % is based onthe total weight of the slurry.

In certain embodiments, a bypass dust slurry comprises one or morefractions of bypass dust where each fraction of bypass dust can becharacterized by a different mean particle size, particle sizedistribution, and/or other property. In certain embodiments, a bypassdust slurry comprises a combination of both fine and coarse bypass dustand the ratio of coarse to fine bypass dust or any other bypass dustfraction can be adjusted to provide a desired reduction in theconcentration of acidic gases. A bypass dust slurry can comprise totalbypass dust where total bypass dust refers to bypass dust that has notbeen separated into fractions based on size or other parameter.

A schematic diagram of certain components of a clinker manufacturingplant that incorporates apparatus for introducing bypass dust into a gasconditioning system is shown in FIG. 5. As described with respect toFIG. 1, kiln feed is introduced to a preheating tower 51 comprisingmultiple separators 52 and a precalciner 53. After entering the rotarykiln 55 the inert volatilized components leave the kiln through kilnriser duct 54. The kiln exhaust contains volatile gases and dust.

The exhaust containing the alkali bypass dust D is cooled to from about900° C. to about 200° C. in a quenching chamber 56, optionally equippedwith additional downstream false air inlets (not shown), by blowing coldair from a quench air fan and drawing in additional false air (notshown). The rapid cooling may cause acidic pollutants such as HCl andSO_(x) entrained in the exhaust gases to condense onto the bypass dustparticles. The quenched exhaust E enters an expansion chamber 57 orother separation apparatus where the bypass dust is separated from thegases. The coarse, separated bypass dust G can be fed back into the kilnfeed, stored in storage 59 for later use, removed, used to make aslurry, and/or introduced into the GCT 515 or any other part of the gasconditioning system between the preheater exit 514 and the main baghouse517 vent.

In an alternative implementation (not illustrated) kiln exhaust gasescontaining cooled or uncooled bypass dust may be routed from kiln exitriser 54 to the preheater exit 514 with injection of the bypass gas andentrained dust near preheater exit 514 and/or the top of the GCT 514.The amount of gas and dust will depend at least in part on the pressuredrop in the preheating tower 51.

If a low efficiency separation apparatus such as an expansion chamber ora static or dynamic separator is used, a second higher efficiencyseparation apparatus such as a baghouse 58 can be used to collect finerbypass dust H. The finer bypass dust H can be fed back into the kilnfeed, stored in storage 59 for later use, removed, used to make ascrubbing slurry and/or introduced into any other part of the systembetween the preheater exit and the main vent baghouse.

The bypass dust G and/or H can be stored in storage 59 and optionallyseparated in a downstream process using separator 510 into a finerbypass dust fraction I and a medium coarse bypass dust fraction J.Again, these fractions can be stored for later use, removed, combinedwith other fractions used to make a slurry and/or introduced into theGCT or any other part of the system between the preheater exit and themain vent baghouse. The fractions can be further separated usingseparator 511 into other fractions such as bypass dust fractions K andM, which can be stored for later use, removed, combined with otherfractions used to make a scrubbing slurry and/or introduced into the GCTor any other part of the system between the preheater exit and the mainvent baghouse.

One or more of the bypass dust fractions can be combined with water inmixer/slaker 513 to provide a slurry O. The slurry O can be introduceddirectly into one or more locations of the gas conditioning system asprovided by mixer/slaker 513 and/or can be mixed with water provided bywater sprays system 519-521.

The apparatus used and routing of the various bypass dust fractionsshown in FIG. 5 is intended to provide an overview of variousembodiments. The apparatus and methods provided by the presentdisclosure are intended to illustrate certain examples and are notintended to be comprehensive. Other apparatus and routing forseparation, combination, and introduction of bypass dust into the gasconditioning system of a clinker kiln can be implemented.

Fine bypass dust fraction M can be introduced into the gas conditioningsystem either dry or combined with water to form a slurry. As shown inFIG. 5, dry fine bypass dust M can be introduced into the gasconditioning system at one and/or more locations. Bypass dust that isnot introduced into the gas conditioning system can be filtered, stored,and/or reintroduced into the mill feed. The fine bypass dust introducedinto the mill feed can provide high surface area free CaO surfaces foradsorption of and reaction with acidic pollutants during the preheatingand precalcination stages, thereby assisting removal of acidicpollutants from the gas stream prior to clinker formation.

The fine bypass dust fraction can be optionally stored in storage 512 orcan be mixed with water in a mixer, slaker, or other mixing apparatus513 to provide a fine bypass dust slurry O. The fine bypass dust slurryO can have, for example, a solids content of from about 20 wt % to 80 wt% such as from about 40 wt % to about 65 wt %. The fine bypass dustslurry O can be pumped into the feed lines of spray lances 18 in the GCTwhere the slurry can optionally be combined with additional water or canbe used as provided from the mixer/slaker 513. A bypass dust slurry canbe introduced into the GCT at a rate from 0.1 gal/min to 150 gal/min,from 75 gal/min to 125 gal/min, or about 100 gal/min, at a solidscontent of fine bypass dust up to about 65 wt %. A suitable rate candepend on factors such as the concentration of the acidic pollutants inthe exhaust, the desired level of scrubbing, the free lime content ofthe fine bypass dust in the lime slurry, and the temperature.

The clinker kiln exhaust conditioning system is primarily used to coolthe exhaust gases leaving the preheater tower prior to separating theparticulates. By introducing free lime CaO and/or hydrated lime Ca(OH)₂into the gas conditioning system, the concentration of particulates andcontrolled acidic pollutants in the exhaust gases from the clinker kilncan be reduced or scrubbed. Exhaust gases comprising particulates andcontrolled acidic pollutants leave the preheater tower 51 and can beintroduced into the inlet of the gas conditioning system at thepreheater exit 514. The conditioned and cooled exhaust gases leave theexit of the gas conditioning tower 515 and are then introduced into adust filter 517. The processed exhaust gases with a reducedconcentration of particulates and controlled acidic pollutants are thenreleased into the atmosphere.

In methods and apparatus provided by the present disclosure, bypass dustcan be introduced into the exhaust conditioning system at one or morelocations. For example, the bypass dust can be introduced in proximityto the exit of the preheater tower, at one or more locations in the gasconditioning tower, in proximity to the entrance of the particulatefilter, or a combination of any of the foregoing. The bypass dust can beintroduced in dry from, wet in the form of a slurry, or both.

Dry bypass dust can be introduced into the exhaust conditioning systemat one or more locations to reduce the concentration of controlledacidic pollutants by about 20% to about 50%, or from about 30% to about40%. Bypass dust in the form of a wet bypass dust slurry can beintroduced into the gas conditioning tower through nozzles situated atone or more locations within the tower. A wet bypass dust slurry can beused to reduce the concentration of controlled acidic pollutants toacceptable levels.

Bypass dust can also be referred to as alkali bypass dust or calcinedbypass dust. The bypass dust can be extracted after calcination in theprecalciner and can be characterized by an active free lime content fromabout 8 wt % to about 80 wt %, such as from about 30 wt % to about 60 wt%. By active free lime CaO content is meant that the bypass dust has ahigh amount of reactive calcium oxide CaO.

The wt % bypass dust in the bypass dust slurry can be selected to obtaina desired reduction in controlled acidic pollutants in the clinker kilnemissions. A suitable wt % can be established based on, for example, thechemical composition of the raw feed, the concentration of thecontrolled acidic pollutants in the exhaust gases, the temperature ofthe exhaust gases at various stages in the gas conditioning system, theflow rate of the exhaust gases in the gas conditioning system, theparticulate content of the exhaust gases, the rate at which the bypassslurry is introduced into the gas conditioning system, the location atwhich the bypass dust is introduced into the gas conditioning system,and other factors. The factors affecting the rate and concentration atwhich the bypass dust is introduced into a gas conditioning system canbe manually or automatically adjusted to provide a suitable level ofcontrolled acidic pollutants in the clinker kiln emissions. Thesefactors can also be influenced by the physical dimensions and layout ofa particular clinker kiln.

It would be possible to use instead of bypass dust, precalciner exitdust that has as well a high percentage of free CaO. That dust would betaken, for example, from separator 52 in FIG. 5.

FIG. 5 shows an example of a clinker kiln in which bypass dust can begenerated and continuously introduced into a gas conditioning systemduring operation of a clinker kiln. Alternatively, bypass dust can begenerated and stored for later use and introduction into the gasconditioning system. For example, in certain embodiments, kiln exhaust Dis cooled in quench air chamber 56, separated in expansion chamber 57,filtered in baghouse 58, and the coarse particulates from expansionchamber 57 and fine particulates collected by the baghouse 58 arecombined and introduced into one or more locations in the gasconditioning system between the preheater exit 514 and the main baghouse517 vent. In certain embodiments, the coarse particulates extracted fromthe expansion chamber are reintroduced into the kiln feed, and the fineparticulates collected by the baghouse are introduced into one or morelocations in the gas conditioning system between the preheater exit 514and the main baghouse 517 vent. In certain embodiments, the coarseparticulates extracted from the expansion chamber are reintroduced intothe kiln feed, and the fine particles from the baghouse are optionallystored, and further separated into a coarse bypass dust fraction, whichcan be reintroduced into the kiln feed, and a fine bypass dust fraction,which can be introduced into one or more locations in the gasconditioning system between the preheater exit 514 and the main baghouse517 vent. In certain embodiments, further to the previous example, thefine bypass dust fraction can be filtered in a baghouse 511, optionallystored in storage 512, and combined with water to form a fine bypassdust slurry, which can be introduced into one or more locations in thegas conditioning system between the preheater exit 514 and the mainbaghouse 517 vent. In certain embodiments, both the coarse bypass dustfraction from expansion chamber 57 and the fine bypass dust fractionfrom baghouse 58 are combined, optionally stored in storage 59, andseparated using separator 510 to provide a coarse bypass dust fractionJ, which can be introduced into one or more locations in the gasconditioning system between the preheater exit 514 and the main baghouse517 vent, and a fine bypass dust fraction I, which can be furtherseparated using separator 511 to provide finer bypass dust fraction M,optionally stored in storage 512, and mixed with water in mixer/slaker513 to provide a fine bypass dust slurry O, which can be introduced intoone or more locations in the gas conditioning system between thepreheater exit 514 and the main baghouse 517 vent. In certainembodiments, the coarse bypass dust from expansion chamber 57 and thefine bypass dust from baghouse 8 can be combined, optionally stored instorage 59, and mixed with water in mixer/slaker 513 to provide a finebypass dust slurry O, which can be introduced into one or more locationsin the gas conditioning system between the preheater exit 514 and themain baghouse 517 vent. Alternatively, only the fine bypass dust frombaghouse 58 can be mixed with water in mixer/slaker 513 to provide afine bypass dust slurry O, which can be introduced into one or morelocations in the gas conditioning system between the preheater exit 514and the main baghouse 517 vent. As an alternative to certain of thepreceding embodiments, expansion chamber 57 may not be used, such thatthe quenched gases and particulates from quench air chamber 56 areintroduced directly into baghouse 58, and the fine bypass dust isoptionally stored, further separated using a separator and/or baghouse,combined with water to form a slurry, and introduced in dry and/or wetform into one or more locations in the gas conditioning system betweenthe preheater exit 514 and the main baghouse 517 vent. In certainembodiments, rather than cool the kiln exhaust with air in a quench airchamber, cooling can be performed using, for example, a water sprayand/or evaporation with or without air cooling.

As an alternative to certain of the preceding embodiments, kiln exitgases containing bypass dust (D) may be redirected to the preheater exit(514) or GCT inlet (518). Those gases can be cooled (E) with ambient airintake or water evaporation or may be used without being cooled. Thisimplementation presents a simple alternative that can be attractive forkilns that do not currently operate a bypass.

The bypass dust can be separated into two or more fractionscharacterized by different particle sizes. For example, the bypass dustcan be separated into a fine bypass dust fraction characterized by anaverage particle diameter less than about 100 microns and a coarsebypass dust fraction characterized by an average particle diametergreater than about 100 microns. The bypass dust can be separated intoother fractions characterized by a particular average maximum and/orminimum particle size diameter and/or average particle sizedistribution. Furthermore, the bypass dust or fraction of the bypassdust can be subjected to further processing such as grinding to modifythe average particle size diameter and/or particle size distribution.

The methods and apparatus provided by the present disclosure are alsoexpected to reduce the concentration of mercury Hg content in the kilnemissions.

FIG. 6 shows a block diagram of certain apparatus used in the processingof bypass dust for use in scrubbing clinker in a gas conditioningsystem. Exhaust gases containing particulates (bypass dust) and volatilegases passing through the precalciner are extracted from the clinkerplant at the kiln riser duct 61. The exhaust gas D is rapidly quenchedto a temperature from about 900° C. to 200° C. with cold air forced intoquenching chamber 63 by quench air fan 62. A certain amount of thecontrolled acidic pollutants such as HCl and SO_(x) entrained in theexhaust gas is absorbed on the cooled particulates. The quenched exhaustgas E enters an expansion chamber 65 or other separation apparatus wherethe particulates entrained in the exhaust are separated from the gas.The expansion chamber can be viewed as a very inefficient separator thatcan be used to classify the particulates by size, density or othercharacteristic. For example, coarse particulates G having an averagediameter greater than about 100 microns can be separated and either fedback into the raw materials forming the kiln feed 68, can be optionallystored in coarse dust storage 69 for later use, or can be fed directlyinto the gas conditioning system L at one or more locations such as, forexample, the preheater exit 623, the gas conditioning tower (GCT) 624,or the baghouse 625. The coarse particles G can also be introduced intomixer/slaker 622 where the particulates are mixed with water to form acoarse bypass dust slurry. The fine particulates F separated byexpansion chamber 65 can be filtered using a baghouse 610 or other dustcollection apparatus such as an electrostatic precipitator. The fineparticulates J can be optionally stored in fine bypass dust storage 613for later use, introduced into the kiln feed (not shown), fed into thegas conditioning system L, optionally combined with coarse bypass dustand/or worked into a slurry.

As shown in FIG. 6, the coarse particulates and the fine particulatescan be fed as coarse bypass dust and fine bypass dust into the gasconditioning system. The amounts of coarse and fine bypass dustintroduced into the gas conditioning system can be determined, in part,by the amounts of controlled pollutants desired to be removed from thekiln exhaust. Furthermore, the coarse and fine bypass dust can beintroduced into the gas conditioning system at one or more locationsbetween the preheater exit 623 and the inlet to baghouse 625. As shownin FIG. 6, coarse bypass dust from optional dust storage 69 can betransported by coarse bypass dust transport system 614 and introducedinto one or more of the preheater exhaust exit 623, the GCT 624, and theinlet to dust collector 625.

Fine bypass dust J can be transported from optional bypass dust storage613 by fine bypass dust transport system 615 and optionally filtered byseparator 616 to further select the size and/or size distribution of theparticulates making up the fine bypass dust. Any rejects K such as largeparticulates and/or agglomerates can be added to the coarse bypass dust,removed or reintroduced into the feed mill and/or the kiln feed. Theseparated fine bypass dust M can be further filtered using baghouse 618to provide finer bypass dust M1. Finer bypass dust M1 can be optionallystored in storage 620, and transported using transport system 621 tomixer/slaker 622 where the finer bypass dust can be optionally combinedwith the coarse bypass dust one or more other bypass dust fractions andwater to form a slurry O, which can be pumped using pump 623 to the GCT624 or into one or more locations between the preheater exit 623 andbaghouse 625. The filtered fine bypass dust M can be optionally storedin storage 620 and transported using transport system 621 tomixer/slaker 622 where the fine bypass dust can be mixed with water toform a fine bypass dust slurry O. The fine bypass dust slurry O can thenbe pumped into the gas conditioning system to reduce the concentrationof controlled pollutants in the exhaust gases. The separated fine bypassdust can further be filtered using a baghouse 618 or other separationapparatus to provide bypass dust M.

FIG. 7 shows a block diagram of certain apparatus used in the processingof bypass dust for use in scrubbing clinker in a gas conditioningsystem. In the apparatus shown in FIG. 7 the bypass dust is notseparated into fine and coarse fractions, such that the unseparatedtotal bypass dust is used to reduce controlled gas emissions.

Exhaust gases containing particulates (bypass dust) and volatile gasespassing through the precalciner are extracted from the clinker plant atthe kiln riser duct 71. The exhaust gas D is rapidly quenched to atemperature from about 900° C. to 200° C. with cold air forced intoquenching chamber 73 by quench air fan 72. A certain amount of thecontrolled acidic pollutants such as HCl and SO_(x) entrained in theexhaust gas is absorbed on the cooled particulates. The quenched exhaustgas E enters an expansion chamber 75 or other separation apparatus wherethe particulates entrained in the exhaust are separated from the exhaustgas.

The particulates F separated by separation device 75 can be filteredusing a baghouse 710 or other dust collection apparatus such as anelectrostatic precipitator. The particulates J can be optionally storedin bypass dust storage 713 for later use, introduced into the kiln feed(not shown), fed into the gas conditioning system L, optionally combinedwith coarse bypass dust and/or worked into a slurry. Total bypass dustcan be transported by bypass dust transport system 1 (714) andintroduced into one or more of the preheater exhaust exit 723,distribution 716, the GCT 724, and/or the inlet to dustcollector/baghouse 725.

The total bypass dust can be transported to bypass dust transport system2 (715) and transported to mixer/slaker 722 where the bypass dust can beoptionally combined with water 79 to form a slurry O, which can bepumped using pump 723 to the GCT 724 or into one or more locationsbetween the preheater exit 723 and baghouse 725.

EXAMPLES

Embodiments provided by the present disclosure are further illustratedby reference to the following examples, which describe the effects ofusing bypass dust to reduce the content of controlled acidic gases inclinker kiln emissions.

A clinker kiln was operated and either lime or bypass dust was injectedinto the GCT to remove acidic pollutants. The results are presented inFIGS. 8-11. In FIGS. 8-11 the molar ratio of either hydrogen chlorideHCl or sulfur oxides SO_(x) emissions to potential mol/h Ca(OH)₂injected into the GCT is presented with potential mol/h Ca(OH)₂ input.

CaO as free lime in bypass dust and hydrated lime Ca(OH)2 are the likelyreactants for the acidic gas components. CaO will react with the coolingwater being injected into the GCT to generate hydrated lime Ca(OH)₂.Therefore, whether hydrated lime or bypass dust is injected into theGCT, it is appropriate to compare the different injections in terms ofpotential Ca(OH)₂ input and permits a direct comparison between the limeslurry and the bypass dust based on the input of Ca(OH)₂ and CaO inputand reflects the demonstration that CaO in the bypass dust can act as anefficient absorber of acidic gases without being transformed intoCa(OH)₂.

Referring to FIGS. 8-11, lime slurry refers to a lime slurry that wasprepared on-site by combining dry Ca(OH)₂ and water to provide a slurryhaving 20 wt % to 40 wt % solids such as from 30 wt % to 40 wt % solids.The Neutralac® SLS45 slurry refers to 45 wt % solids commerciallyavailable lime slurry obtained from LHoist North America. All limetrials refer to trials in which Ca(OH)₂ was injected into the GCT, whichcan differ in the point of injection but were within about 8 inches. Theregression curve for all lime trials is also shown.

Referring to FIGS. 8-11, fine bypass dust slurry refers to a 20 wt % to40 wt %, solids, such as from 30 wt % to 40 wt % solids slurry preparedfrom a fine bypass dust fraction generally having a particle size lessthan 80 μm. Total bypass dust slurry refers to a 20 wt % to 40 wt %solids slurry prepared from the total bypass dust. All Bypass Dust (1)and All Bypass Dust (2) refer to results obtained by injecting totalbypass dust into the GCT. In Total Bypass Dust (1) the dust was injectedthrough a single nozzle just above the water injection ports; and in AllBypass Dust (2) the dust was injected well above the water injectionports and above buffer blades through multiple nozzles. Therefore, thepoints of injection for the All Bypass Dust (1) and All Bypass Dust (2)runs were substantially different (compared the All lime trialsdiscussed above, which were within about 8 inches of each other). Theregression lines for All Bypass Dust (1) and All Bypass Dust (2) areshown in the figures.

In FIGS. 8-11 a high acidic emission of either hydrogen chloride HCl orsulfur oxides SO_(x), or a very low Ca(OH)₂ input will result in a highratio. Due to dust recirculation at the preheater exit there will alwaysbe at least some potential Ca(OH)₂ in the form of free lime CaO presentin the dust leaving the tower. The graphs show that with no Ca(OH)₂injection there is a high acidic content, and with increasing potentialCa(OH)₂ input either in the form of hydrated Ca(OH)₂ in dry or slurryform or as bypass dust (CaO and Ca(OH)₂) in dry or slurry form theacidic emissions are reduced. By comparing the regression curves, it canbe appreciated that bypass dust injection is more efficient at removinghydrogen chloride HCl and sulfur oxides SO_(x) from the kiln gas than isdry lime or any slurry. The dramatic improvement in the efficiency forthe All Bypass Dust (2) injection compared to All Bypass Dust (1)injection demonstrates that adjustments to the implementation of bypassdust injection can lead to increased scrubbing efficiency.

FIG. 9 re-presents the data presented in FIG. 8 extended to highereffective Ca(OH)₂ input and includes the regression curve for limeslurry. As shown in FIG. 9, the dry lime injection and the lime slurryhave a similar effect on reducing hydrogen chloride HCl emission. Theinjection of dry lime in general exhibits better efficiency at highhydrogen chloride HCl concentrations and lime slurry has betterefficiency at lower hydrogen chloride HCl concentrations.

FIGS. 10 and 11 show that All Bypass Dust (2) injection is also moreefficient than lime at removing sulfur oxides SO_(x) from the kilnexhaust; and the dry lime is a little more efficient than lime slurry inremoving sulfur oxides from kiln emission.

In aspects of the invention, methods for reducing the concentration ofcontrolled pollutants in clinker kiln emissions comprise providing aclinker kiln, wherein the clinker kiln comprises a gas conditioningsystem configured to process exhaust gases from the clinker kiln; andintroducing bypass dust generated during operation of the clinker kilnat one or more locations in the gas conditioning system, to reduce theconcentration of controlled pollutants in the clinker kiln emissions.

In any of the preceding aspects, the gas conditioning system comprises apreheater exhaust exit; a gas conditioning tower operatively coupled tothe preheater exhaust exit; and an inlet to a dust collector.

In any of the preceding aspects, introducing the bypass dust comprisesintroducing the bypass dust in proximity to the preheater exhaust exit,into the gas conditioning tower, in proximity to the inlet to the dustcollector, or a combination of any of the foregoing.

In any of the preceding aspects, the bypass dust comprises alkali-bypassdust.

In any of the preceding aspects, the bypass dust comprises calcinedbypass dust and partially calcined bypass dust.

In any of the preceding aspects, the controlled pollutants comprisecontrolled acidic pollutants.

In any of the preceding aspects, the bypass dust comprises fine bypassdust characterized by an average particle size less than 100 microns.

In any of the preceding aspects, the bypass dust comprises fine bypassdust characterized by an average mean particle diameter from 4 micronsto 80 microns.

In any of the preceding aspects, the bypass dust comprises total bypassdust.

In any of the preceding aspects, the bypass dust is characterized by acalcium oxide (CaO) content from 8 wt % to 80 wt %, wherein wt % isbased on the total solids content of the bypass dust.

In any of the preceding aspects, the bypass dust comprises a bypass dustslurry, wherein the bypass dust slurry comprises bypass dust and water.

In any of the preceding aspects, the bypass dust comprises a fine bypassdust slurry, wherein the fine bypass dust slurry comprises fine bypassdust characterized by an average particle size less than 100 microns,and water.

In any of the preceding aspects, the fine bypass dust slurry ischaracterized by a solids content from 20 wt % to 80 wt %, wherein wt %is based on the total weight of the fine bypass dust slurry.

In any of the preceding aspects, the methods further comprise separatingthe bypass dust into coarse bypass dust and fine bypass dust, whereinintroducing bypass dust comprises introducing coarse bypass dust,introducing fine bypass dust, or introducing a combination thereof.

In any of the preceding aspects, the coarse bypass dust is characterizedby an average mean particle diameter greater than 100 μm; and the finebypass dust is characterized by an average mean particle diameter lessthan 100 μm.

In any of the preceding aspects, the fine bypass dust is characterizedby an average mean particle diameter from 2 microns to 40 microns; andthe coarse bypass dust is characterized by an average mean particlediameter from 20 microns to 80 microns.

In any of the preceding aspects, the fine bypass dust is characterizedby a calcium oxide (CaO) content from 25 wt % to 80 wt %, wherein wt %is based on the total weight of the fine bypass dust.

In any of the preceding aspects, introducing the bypass dust comprisesintroducing the coarse bypass dust into the gas conditioning tower;introducing the fine bypass dust into the gas conditioning tower; orintroducing both the coarse bypass dust and the fine bypass dust intothe gas conditioning tower.

In any of the preceding aspects, introducing the bypass dust comprisesintroducing the coarse bypass dust in proximity to the preheater exhaustexit, into one or more locations in the gas conditioning tower, inproximity to the inlet of the dust collector, or a combination of any ofthe foregoing; and introducing the fine bypass dust into the gasconditioning tower.

In any of the preceding aspects, methods further comprise mixing thefine bypass dust with water to provide a fine bypass dust slurry; andintroducing the fine bypass dust slurry into the gas conditioning tower.

In any of the preceding aspects, the fine bypass dust slurry ischaracterized by a solids content from 20 wt % to 80 wt %, wherein wt %is based on the total weight of the fine bypass dust slurry.

In aspects of the invention, a clinker plant comprises a gasconditioning system comprising a preheater exit, a gas conditioningtower, and a main baghouse; one or more separators for separating dustgenerated during the production of clinker into one or more dustfractions; and an injector for introducing at least one of the one ormore dust fractions into the gas conditioning system at one or morelocations between the preheater exit and the main baghouse.

In any of the preceding aspects, a clinker plant further comprises amixer configured to combine water and at least one of the one or moredust fractions to provide a dust slurry.

In any of the preceding aspects, the injector is configured to introduceat least one of the more dust fractions comprises introducing a dustslurry at one or more locations between the preheater exit and the mainbaghouse.

In an aspect of the present invention, methods for reducing theconcentration of controlled pollutants in clinker kiln emissions,comprise providing a clinker kiln, wherein the clinker kiln comprises agas conditioning system configured to process exhaust gases from theclinker kiln; and introducing dust generated during operation of theclinker kiln at one or more locations in the gas conditioning system, toreduce the concentration of controlled pollutants in the clinker kilnemissions.

In any of the preceding aspects, the gas conditioning system comprises apreheater exhaust exit; a gas conditioning tower operatively coupled tothe preheater exhaust exit; and an inlet to a dust collector.

In any of the preceding aspects, introducing the bypass dust comprisesintroducing the bypass dust in proximity to the preheater exhaust exit,into the gas conditioning tower, in proximity to the inlet to the dustcollector, or a combination of any of the foregoing.

In any of the preceding aspects, the dust comprises bypass dust.

In any of the preceding aspects, the dust comprises calcined dust andpartially calcined dust.

In any of the preceding aspects, the controlled pollutants comprisecontrolled acidic pollutants.

In any of the preceding aspects, the dust comprises total dust separatedfrom the kiln exhaust

In any of the preceding aspects, the dust is characterized by a calciumoxide (CaO) content from 8 wt % to 80 wt %, wherein wt % is based on thetotal solids content of the dust.

In any of the preceding aspects, the methods further comprise separatingthe dust into coarse dust and fine dust, wherein introducing dustcomprises introducing coarse dust, introducing fine dust, or introducinga combination thereof.

In any of the preceding aspects, the coarse dust is characterized by anaverage mean particle diameter greater than 100 μm; and the fine dust ischaracterized by an average mean particle diameter less than 100 μm.

In any of the preceding aspects, introducing the dust comprisesintroducing the coarse dust into the gas conditioning tower; introducingthe fine dust into the gas conditioning tower; or introducing both thecoarse dust and the fine dust into the gas conditioning tower.

In any of the preceding aspects, the methods further comprise mixing thefine dust with water to provide a fine dust slurry; and introducing thefine dust slurry into the gas conditioning tower.

According to the present invention, a clinker plant comprises a gasconditioning system comprising a preheater exit, a gas conditioningtower, and a main baghouse; a separator for separating dust from exhaustgases; and a nozzle for introducing the separated dust in proximity tothe preheater exhaust exit, into the gas conditioning tower, inproximity to the inlet to the dust collector, or a combination of any ofthe foregoing.

In any of the preceding aspects, the clinker plant further comprises oneor more separators for separating dust generated during the productionof clinker into one or more dust fractions.

In any of the preceding aspects, the clinker plant further comprises aslaker for mixing the one or more dust fractions with water to provide adust slurry; and a nozzle for introducing the dust slurry into the gasconditioning tower.

In any of the preceding aspects, the clinker plant further comprises anozzle for introducing at least one of the one or more dust fractionsinto the gas conditioning system at one or more locations between thepreheater exit and the main baghouse.

Finally, it should be noted that there are alternative ways ofimplementing the embodiments disclosed herein. Accordingly, the presentembodiments are to be considered as illustrative and not restrictive.Furthermore, the claims are not to be limited to the details givenherein, and are entitled their full scope and equivalents thereof.

What is claimed is:
 1. A clinker plant comprising: a clinker kiln; akiln exit riser coupled to the clinker kiln, wherein the kiln exit risercomprises a kiln riser duct; a precalciner coupled to the kiln exitriser; a preheater coupled to the precalciner, wherein the preheatercomprises a preheater exit; and one or more apparatus configured tointroduce bypass dust extracted from the kiln riser duct into preheaterexhaust gases leaving the preheater exit.
 2. The clinker plant of claim1, wherein the apparatus comprises: one or more separators configured toseparate the bypass dust from kiln exhaust; one or more separatorsconfigured to separate the bypass dust into one or more bypass dustfractions; one or more slakers configured to provide one or more bypassdust slurries; one or more nozzles configured to introduce the bypassdust into the preheater exhaust gases; or a combination of any of theforegoing.
 3. The clinker plant of claim 1, wherein the bypass dustcomprises coarse bypass dust, fine bypass dust, or a combinationthereof.
 4. The clinker plant of claim 1, comprising one or moreseparators configured to separate the bypass dust into one or morebypass dust fractions.
 5. The clinker plant of claim 1, comprising oneor more separators configured to separate the bypass dust into a coarsebypass dust fraction and a fine bypass dust fraction.
 6. The clinkerplant of claim 5, wherein, the coarse dust is characterized by anaverage mean particle diameter greater than 100 μm; and the fine dust ischaracterized by an average mean particle diameter less than 100 μm. 7.The clinker plant of claim 1, comprising one or more separatorsconfigured to separate the bypass dust into a fine bypass dust fraction,and wherein the one or more apparatus configured to introduce bypassdust comprises an apparatus configured to introduce the fine bypass dustfraction into the preheater exhaust gases.
 8. The clinker plant of claim1, comprising one or more separators configured to separate the bypassdust into a coarse bypass dust fraction, and wherein the one or moreapparatus configured to introduce bypass dust comprises an apparatusconfigured to introduce the coarse bypass dust fraction into thepreheater exhaust gases.
 9. The clinker plant of claim 1, comprising:one or more separators for separating the bypass dust into a coarsebypass dust fraction; and one or more slakers for providing one or morecoarse bypass dust slurries; and wherein the one or more apparatusconfigured to introduce bypass dust comprises an apparatus configured tointroduce the one or more coarse bypass dust slurries into the preheaterexhaust gases.
 10. The clinker plant of claim 1, wherein the apparatuscomprises one or more separators for separating the bypass dust into oneor more bypass dust fractions; and wherein each of the one or moreapparatus is configured to introduce at least one of the one or morebypass dust fractions into the preheater exhaust gases.
 11. The clinkerplant of claim 1, wherein the apparatus comprises: one or moreseparators for separating the bypass dust into a first bypass dustfraction and a second bypass dust fraction; one or more slakers forproviding a slurry comprising the first bypass dust fraction; andwherein the one or more apparatus configured to introduce bypass dustcomprises: a first apparatus configured to introduce the slurry into thepreheater exhaust gases; and a second apparatus configured to introducethe second bypass dust fraction into the preheater exhaust gases. 12.The clinker plant of claim 1, wherein the bypass dust comprises drybypass dust, a slurry comprising bypass dust, or a combination thereof.13. The clinker plant of claim 1, wherein the bypass dust comprises aslurry of coarse bypass dust, a slurry of fine bypass dust, or acombination thereof.
 14. The clinker plant of claim 1, wherein thebypass dust is characterized by a calcium oxide (CaO) content from 8 wt% to 80 wt %, wherein wt % is based on the total solids content of thebypass dust.
 15. The clinker plant of claim 1, wherein the one or moreapparatus configured to introduce bypass dust extracted from the kilnriser duct into preheater exhaust gases are configured to introduce thebypass dust into the preheater exhaust gases at different locations.